1. Field of the Invention
This invention relates to oil and gas well drilling and safety valves used in oil and gas well drilling. More specifically, the instant invention resides in the provision of an inside blowout preventer valve which is automatically closed as a result of a reduction of the velocity of drilling fluid moving downwardly therethrough and which may be plugged while in the open position through the utilization of a plug retrievable by an overshot tool.
2. Description of Related Art
Various different forms of inside blowout preventer valves and kelly valves including some of the general structural and operational features of the instant invention heretofore have been provided.
Examples of these different forms of previously known valves are disclosed in U.S. Pat. Nos. 3,086,764, 3,292,718, 3,750,751, 3,763,940, 3,768,506, 3,901,321, 3,915,228, 4,086,935, 4,262,693, 4,303,100, 4,316,596, 4,361,188, 4,467,870, 4,475,598, 4,519,576, 4,550,780, 4,552,219 and 4,569,397.
However, the blowout preventer valve of the instant invention constitutes a non-complex valve which is fully operative in the intended manner and which defines a large diameter passage therethrough, when open, to thereby provide minimum resistance to drilling fluid passing therethrough.